The burner assembly as described within this disclosure is utilized in that capacity generally defined as a direct-fired gas industrial or related type of air heater. This is not a heat exchanger, since the combustion of the gas after its ignition takes place directly within the air stream being heated, and not by conduction thereof. Hence, the heating equipment contains no flue, and all of the by-products of the combustion are released into the heated air stream, which is then directly discharged into the space being heated, and as a result it is desirable, and one of the primary advantages of this current invention, to provide means for reducing the creation and release of deleterious exhaust or gases, either in the form of carbon monoxide, or nitrogen dioxide, that is discharged during the gas combustion, and to reduce it to a minimum in order to minimize the amount of foul odors that may be directed into the space being heated, and certainly to alleviate the likelihood that any persons therein may be harmed through the breathing of such gases over a sustained period of time.
Direct-fired gas heaters typically are constructed in a variety of configurations. The majority of such heaters, as manufactured, are located with the burner being arranged upstream of the fan inlet, and which functions in a draw-through arrangement. A number of other manufacturers position the burner downstream of the fan or blower discharge, in what is defined as blow-through arrangement. An example of the latter can best be seen in the U.S. Pat. No. 3,630,499, which is owned by a common assignee to the improved burner of this current invention.
As is well known in this art, the performance characteristics of the burner necessarily determines the operational range of the heating equipment, when tested, to gauge whether it is in compliance with the various requirements of the American National Standards Institute (ANSI), governing the functioning of the direct gas-fired industrial air heaters, of the type of this invention. This is generally set forth in the ANSI standard Z83.18. Generally, the air flow through a heater of this type, and the temperature rise that occurs for the air that is being heated, determines the heating capacity of the subject unit. The air flow is directly related to the fan as selected, the motor horse power of the unit driving the fan, and the static pressure on the system during its functioning. The temperature rise is controlled by the gas flow delivered to the burner, at the given air flow rate for the capacity of air that has been blown through the unit, as induced by the blower.
As previously explained, the ANSI standards generally provide an industry self regulation of the minimum requirements that must be met by units of this design. These standards generally allow for specific maximum additive levels of four particular products of combustion that may be released from a heating unit of this type during its functioning. These products of combustion and respective allowable levels are as follows: carbon dioxide, 4,000 parts per million (ppm); carbon monoxide, 5 ppm; aliphatic aldehydes, 1.0 ppm; and, nitrogen dioxide, 0.50 ppm. These particular derived chemical compounds, which are generally recognized as undesirable by-products from the functioning of heating units of this type, and their gases of combustion, can basically be defined as unwanted derivatives, which, if they can be reduced to a minimum, not only add to the safety of all people within the heated space, but enhances the quality operations of the heating unit, as designed. The unit of this particular invention has been designed to provide for a minimization of the output of these undesirable compounds, through the unique design of particular characteristics and features built into the improved heater of this invention, to attain such desirable results.
It has been determined through testing that there are three major factors that effect the production of carbon monoxide within the gas combustion production process. Ideally, the gas and combustion air needs to be mixed as completely and thoroughly as possible as soon after the gas is introduced into the burner assembly. If too little combustion air is introduced into the burner, then incomplete combustion occurs. This raises the level of carbon monoxide output, which can easily be measured in the discharge air stream. On the other hand, if too much combustion air is introduced into the combustion process, quenching of the flame can occur, and this abrupt cooling also causes incomplete combustion. Thus, an equilibrium point desirably must be reached with respect to how much air is introduced into the burner, in combination with the amount of gas discharged from the manifold, and the location and implacement of the air intake into the combustion zone.
An additional factor which affects the development of carbon monoxide in the burning process is also related to this quenching feature of the flame, but in this particular case, with respect to this heater, the concern is with the abrupt cooling of the flame after it exits from the burner. In units of this type, the discharge air pattern leaving the fan or blower results in a greater volume of air in the upper region of the fan discharge. With the burner downstream of the blower, the burner acts as a restriction to the flow of air, thereby compressing the air, causing the velocity to increase as it passes the burner. Once the restriction is passed, the large volume of air from the upper portion of the duct expands rapidly to equalize pressure within the duct causing the cool air to impinge the flame tips that are extending beyond the end of the burner. This type of air impingement causes a quenching of the flame in prior art devices, and had increased CO output.
The manner in which the air is introduced into the burner is a factor which is just as important as to how much air is introduced into the same. It has been found that the output level of carbon monoxide can readily be reduced by limiting the amount of combustion air early in the burner, near the gas ports, and supplying more air later, or further downstream, within the burner assembly. Thus, combustion takes place early in the burner at low combustion rates. With high combustion rates, as when an abundance of gas is introduced through the manifold, such combustion takes place more thoroughly throughout the whole burner assembly and more downstream from the intake gas manifold. Therefore, at lower combustion rates, less gas and less air will by necessity be needed to support such combustion. Also, at higher combustion rates, when more air is needed, it is preferably supplied more downstream in the burner assembly.
The current invention has been designed to take into consideration these various features, and to not only regulate the amount, capacity, and particularly location of the quantity of gas being ejected from the manifold into the chamber of combustion, but likewise, to provide for its adequate positioning, within the area of combustion, and to inject the adequate amount of air to augment combustion, at particular locations, and at specific amounts, in order to enhance the efficiency of combustion, and thereby reduce the development of carbon monoxide.
In addition to the foregoing, the subject matter of this invention further contemplates modifications to the structure of the burner embodiment, and more specifically its various formed chambers, in order to minimize the amount of heat exposure of the various walls and chambers, in addition to adding modifications to select baffled tiers to better isolated areas of desired maximum combustion, to reduce the development of hot spots upon the various structure walls, and thereby, which has been found through experimentation and research, to significantly reduce the development of nitrogen dioxide, and its emission, from the burner of this invention during its functioning.